The Internet Protocol Multimedia Subsystem (“IMS”), developed by the standards organization known as the 3rd Generation Partnership Project (“3GPP”), is an architectural framework for delivering Internet Protocol (“IP”) multimedia to mobile users, such as users of various mobile devices. An IMS core network (“IMS core”) allows wireless and wireline devices to access multimedia, messaging, and voice applications and services. To ease the integration of an IMS core with Internet resources, 3GPP specifications use Internet Engineering Task Force (“IETF”) protocols, such as the Session Initiation Protocol (“SIP”) and Diameter, within the IMS core.
The IMS core, as defined in the 3GPP TS 23.167 specification, supports emergency services by routing emergency calls (e.g., “911” calls) to the nearest Public Safety Answering Point (PSAP), which is a physical location that receives emergency calls from the public.